\begin{tikzpicture}[>=Stealth]
    % 各坐标点的相对位置
    %
    %          M
    %          C
    %               B
    %   N
    %   A
    \pgfmathsetmacro{\factor}{0.3}
    \pgfmathsetmacro{\nac}{45}
    \pgfmathsetmacro{\ac}{10 * \factor}
    \pgfmathsetmacro{\mcb}{105}

    \pgfmathsetmacro{\mca}{180 - \nac}
    \pgfmathsetmacro{\acb}{360 - \mca - \mcb}
    \pgfmathsetmacro{\cab}{asin(sin(\acb) * 9/21)}% V_cb : V_ab
    \pgfmathsetmacro{\cba}{180 - \cab - \acb}
    \pgfmathsetmacro{\ab}{\ac * sin(\acb) / sin(\cba)}

    \coordinate ["$A$" below] (A) at (0, 0);
    \coordinate ["$B$" right] (B) at (90 - \nac - \cab:\ab);
    \coordinate ["$C$" above left] (C) at (90 - \nac:\ac);

    \draw [very thick] (A) -- (B) -- (C) -- cycle;

    \draw [->] (C) -- +(0, 1) coordinate (M) node [above] {北}
        pic [draw, solid, <-, angle radius=0.8em, "$105^\circ$" {xshift=0.5em}, angle eccentricity=1.8] {angle=B--C--M};

    \draw [->] (A) -- +(0, 2) coordinate (N) node [above] {北}
        pic [draw, solid, <-, angle radius=1.5em, "$45^\circ$" {yshift=0.2em}, angle eccentricity=1.3] {angle=C--A--N};
    \draw pic [draw, solid, <-, angle radius=2.9em, "$?$", angle eccentricity=1.3] {angle=B--A--N};

    \coordinate (M) at ($(B) + (0.7, -0.6)$);
    \pic [scale=0.03] at (M) {mountain};
\end{tikzpicture}

